This invention relates to a dot impact printer controller, more specifically to a controller that stores and updates self-adjustment data in order to maintain good print quality for the guaranteed life of the print head.
Dot impact printers are widely used in information-processing equipment because they combine relatively low cost with the ability to print on varied media. The print head of a dot impact printer is equipped with movable dot wires that press an ink ribbon against the printing medium, thereby printing dots. Print heads are classified as plunger-driven, spring-charged, or clapper-type. In a spring-charged print head, the dot wires are actuated by a mechanism comprising a permanent magnet, plate springs, and electromagnets. Conventionally, the printer is tested when manufactured and its controller is adjusted to provide exciting current pulses of an appropriate duration to the electromagnets. The pulse duration is not normally readjusted unless the printer is returned to the manufacturer for service.
During the life of a print head, the dot wires, electromagnet cores, and other parts of the printer are liable to wear down, increasing the gap between the printing medium and the dot wires, and causing possible printing problems such as missing dots. When the current pulse duration is adjusted at the factory, it is therefore adjusted not to the optimal value but to an intentionally longer value, to ensure that adequate current will be fed to the electromagnets to print each dot during the entire guaranteed life of the print head. This overdriving of the electromagnets has certain drawbacks, however, including unnecessary power consumption, unnecessary noise, and overheating of the print head.